Over the past year I've received several invitations to LinkedIn from people I know. Before clicking anything I checked with them. Each had not sent the invitation.
As a real estate agent I keep my politics out of any discussions with potential clients. But if they bring it up, I'll ask if it really matters. If it does, they'll get the truth.
LinkedIn is being ‘spammed’ by fake invitations. These fakers usually take a photo off of linkedIn (or the web) and build a fake profile. They want you to “accept” so they can glean your information and then spam you via other means. . .like email or telemarketers.
LinkedIn is really quick about banning/blocking offending ISPs.